A conventional wavelength division multiplexer ("WDM") is used to combine or separate optical signals having different wavelengths. For example, a three port WDM can be used to combine two optical signals or to separate an incoming signal into two components which have two different wavelengths.
In optical communications, conventional WDMs have many applications. For example, conventional WDMs are often used in optical amplifiers, in which a signal having one wavelength, such as 1550 nanometers ("nm"), can be amplified by combining the signal with a pumping source, for example, a pumping source having a wavelength of 980 nm or 1480 nm. Another application for WDMs is simultaneous transmission of a plurality of optical signals over a single fiber. A conventional WDM combines the signals having wavelengths of 1310 nm and 1550 nm prior to transmission over the single fiber and separates the signals at the receiver.
A large cost in optical technology is the cost of providing optical fibers to carry the optical signal between points. To reduce this cost, there is a trend towards carrying more signals on a single fiber rather than providing additional fibers. As a result, the demand for WDMs used to separate or combine such signals has dramatically increased. As the number of signals per fiber increases, the wavelength of each signal becomes closer to the wavelength of neighboring signals. In response to this decrease in spacing between signals, dense WDMs have been developed. Dense WDMs typically separate or combine optical signals having only small differences in wavelength. The difference between wavelengths of neighboring signals in a dense WDM is typically less than 3.2 nm.
In addition to combining and separating closely spaced signals, WDMs must be reliable and perform well in the environment in which they are placed. For example, there are always transmission losses associated with a conventional WDM. These transmission losses should be small and remain constant throughout operation of the WDM. However, the temperature of the environment in which the WDM operates can vary. Thus, a WDM should have a small transmission loss which is relatively insensitive to temperature. A WDM should also be reliable. Consequently, Bellcore standards for optical components, which concern the reliability of optical components, should also be met.
Although a conventional WDM can separate or combine signals, the reliability and performance of the WDM can be affected by the packaging of the WDM. Typically, in the case of micro-optic WDMs which are based on collimators and thin-film filters, the collimators of a WDM are held in place by epoxy. The epoxy may have a temperature dependence and may not be mechanically reliable. Consequently, the WDM will not have sufficient performance or reliability.
Accordingly, what is needed is a system and method for providing a WDM which has improved reliability. The present invention addresses such a need.